Heretofore, as a working fluid for heat cycle such as a refrigerant for a refrigerator, a refrigerant for an air-conditioning apparatus, a working fluid for a power generation system (such as exhaust heat recovery power generation), a working fluid for a latent heat transport apparatus (such as a heat pipe) or a secondary cooling fluid, a chlorofluorocarbon (CFC) such as chlorotrifluoromethane (CFC-13) or dichlorodifluoromethane (CFC-12), or a hydrochlorofluorocarbon (HCFC) such as chlorodifluoromethane (HCFC-22) has been used. However, influences of CFCs and HCFCs over the ozone layer in the stratosphere have been pointed out, and their use is regulated at present.
In this specification, abbreviated names of halogenated hydrocarbon compounds are described in brackets after the compound names, and in this specification, the abbreviated names are employed instead of the compound names as the case requires.
Under the above conditions, as a working fluid for heat cycle, a hydrofluorocarbon (HFC) which has less influence over the ozone layer, such as difluoromethane (HFC-32), tetrafluoroethane (HFC-134) or pentafluoroethane (HFC-125), has been used instead of CFCs and HCFCs. For example, R410A (a pseudoazeotropic mixture refrigerant of HFC-32 and HFC-125 in a mass ratio of 1:1) is a refrigerant which has been widely used. However, it has been pointed out that HFCs may cause global warming. Accordingly, development of a working fluid for heat cycle which has less influence over the ozone layer and has a low global warming potential (GWP) is an urgent need.
In recent years, as a working fluid for heat cycle which has less influence over the ozone layer and has less influence over global warming, a hydrofluoroolefin (HFO) having a carbon-carbon double bond which is easily decomposed by OH radicals in the air has been expected. In this specification, a saturated HFC is represented as a HFC and is distinguished from a HFO having a carbon-carbon double bond unless otherwise specified.
As a working fluid using a HFO, for example, Patent Document 1 discloses a composition containing trifluoroethylene (HFO-1123). Patent Document 1 discloses use of HFO-1123 with various HFCs or HFOs in combination for the purpose of increasing the flame retardancy, the cycle performance, etc. of the working fluid.
As mentioned above, a working fluid containing HFO-1123, which is excellent in the cycle performance, has been desired.
HFO-1123 is produced by various processes, and impurities are present in the formed product by any production process. And, if such HFO-1123 containing impurities (hereinafter sometimes referred to as crude HFO-1123) is used as it is, a working fluid excellent in the cycle performance may not be obtained in some cases.
Accordingly, to use HFO-1123 for a working fluid, a step of reducing impurities from the crude HFO-1123 is essential.